Make istreambuf_iterator::_M_sbuf immutable and add debug checks

[Jonathan Wakely]

On 16/11/17 08:51 +0300, Petr Ovtchenkov wrote:
>On Mon, 6 Nov 2017 22:19:22 +0100
>François Dumont <frs.dumont@gmail.com> wrote:
>
>> Hi
>>
>>  Â Â Â  Any final decision regarding this patch ?
>>
>> François
>
>https://gcc.gnu.org/ml/libstdc++/2017-11/msg00036.html
>https://gcc.gnu.org/ml/libstdc++/2017-11/msg00035.html
>https://gcc.gnu.org/ml/libstdc++/2017-11/msg00037.html
>https://gcc.gnu.org/ml/libstdc++/2017-11/msg00034.html

It would be helpful if you two could collaborate and come up with a
good solution, or at least discuss the pros and cons, instead of just
sending competing patches.